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//! Misc utilities used by library

use std::fmt;
use std::io::{self, Write};
use std::mem;

pub(crate) struct BytesWriter {
    buf: bytes::BytesMut,
}

impl BytesWriter {
    #[inline]
    pub fn new() -> Self {
        Self::with_capacity(0)
    }

    #[inline]
    pub fn with_capacity(capacity: usize) -> Self {
        Self {
            buf: bytes::BytesMut::with_capacity(capacity)
        }
    }

    #[inline]
    pub fn freeze(&mut self) -> bytes::Bytes {
        mem::replace(&mut self.buf, bytes::BytesMut::new()).freeze()
    }
}

impl io::Write for BytesWriter {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.buf.extend_from_slice(buf);
        Ok(buf.len())
    }

    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        self.buf.extend_from_slice(buf);
        Ok(())
    }

    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

///Transforms `Display` into `HeaderValue`
pub fn display_to_header<T: fmt::Display>(data: &T) -> http::header::HeaderValue {
    let mut res = BytesWriter::new();
    let _ = write!(&mut res, "{}", data);
    unsafe { http::header::HeaderValue::from_shared_unchecked(res.freeze()) }
}